The present invention relates to a novel ferroelectric commercial size single crystal wafer having a high dielectric constant together with high electromechanical and electrooptical properties and a process for the preparation thereof.
Single crystals having a high ferroelectric constant and small temperature dependency are particularly useful for preparing such devices as ultrasonicators, actuators, microphones, surface acoustic wave(SAW) elements, optical modulators and optical switches.
Since G. A. Smolenskii et al. reported that a single crystal of lead magnesium niobate (Pb(Mg⅓Nb⅔)O3; xe2x80x9cPMNxe2x80x9d) is such a strongly ferroelectric material in Sov. Phys. Solid State Vol. 1, 1429 (1959), many processes for the preparation of PMN have been reported. Recently, Sang-goo Lee et al. has succeeded in growing PMN to a size of about 1 cm (see Appl. Letts. Vol. 74, No. 7, 1030 (1999)) using the Bridgemann method, and Luo has reported the growth and the properties of a PMN-PT (0.67Pb(Mg⅓Nb⅔)O3-0.33PbTiO3) single crystal having a diameter of 2.5 cm in 1999 IEEE Ultrasonic Symposium-1009.
In order for a single crystal to possess a commercial value, it should be grown to a size of greater than 5 cm in diameter. However, ferroelectric single crystals have not been successfully grown to such a large size.
Therefore, there has existed a need to develop a strongly ferroelectric single crystal which can be grown to a size greater than 5 cm in diameter.
It is, therefore, a primary object of the invention to provide a novel ferroelectric single crystal wafer of a commercializable size having a high dielectric constant together with good electromechanical and electro-optical properties.
In accordance with an aspect of the present invention, there is provided a ferroelectric single crystal wafer having the composition of formula (I):
x(A)y(B)z(C)-p(P)n(N)xe2x80x83xe2x80x83(I)
wherein,
(A) is Pb(Mg⅓Nb⅔)O3 or Pb(Zn⅓Nb⅔)O3,
(B) is PbTiO3,
(C) is LiTaO3,
(P) is a metal selected from the group consisting of Pt, Au, Ag, Pd and Rh,
(N) is an oxide of a metal selected from the group consisting of Ni, Co, Fe, Sr, Sc, Ru, Cu and Cd,
x is a number in the range of 0.65 to 0.98,
y is a number in the range of 0.01 to 0.34,
z is a number in the range of 0.0 1 to 0. 1, and
p and n are each independently a number in the range of 0.01 to 5.
In accordance with another aspect of the present invention, there is provided a process for preparing the ferroelectric single crystal wafer having the composition of formula (I), which comprise the steps of:
(a) mixing a component selected from Pb(Mg⅓Nb⅔)O3 and Pb(Zn⅓Nb⅔)O3 with PbTiO3, and LiTaO3, in relative molar amounts ranging from 0.65 to 0.98, 0.01 to 0.34 and 0.01 to 0.1, respectively,
(b) adding, to the mixture obtained in (a), a metal selected from the group consisting of Pt, Au, Ag, Pd and Rh, and an oxide of a metal selected from the group consisting of Ni, Co, Fe, Sr, Sc, Ru, Cu and Cd, in amounts ranging from 0.01 to 5% by weight based on the mixture,
(c) calcining the mixture obtained in (b), followed by pulverizing the calcination product,
(d) melting the powder obtained in (c), and
(e) cooling the melt to crystallize.